Temperatures today and tomorrow in the D.C. will be unseasonably cold, with overnight lows in the 20s and daytime temperatures not exceeding 40 to 45 degrees. The last time it was colder than this in November was 2008.

On November 22, 2008 the high at Reagan National only managed 37, with a morning low of 26. This day occurred in the midst of a very cool second half of the month, when 13 out of the 15 days had highs below 50. Contrast that with the relatively mild Novembers from 2009 to 2011 which had not a single day with highs below 50.

Last year (2012), November was a bit chillier, with 5 sub-50 days. But even November 2012’s coldest day – with a high of 43 and low of 33 on the 25th – will probably be warmer than tomorrow’s temperatures.

Tomorrow’s high at Reagan National should be somewhere between 41 and 44, with lows 28-31.

Forecast highs from the GFS model Wednesday afternoon (WeatherBell.com)

According to the Southeast Regional Climate Center, such readings would rank around the 4th coldest on record since 1929 and most closely resemble the normals for Portland, Maine for the date. They’ll roughly match our coldest temperatures experienced last March. Our last day decidedly colder than this occurred all the way back on February 22 (with a high of 35 and low of 31).

The normal high and low for November 13 in Washington, D.C. is 59 and 42, so these temperatures are about 15 degrees below what we expect.

What’s behind the cold?

An extremely strong Arctic air mass has plunged into the central U.S. and its cold air is bleeding southeastward. Some analyses have indicated the pressure – an indicator of the strength of the air mass- is 1047 millibars near the core – which is unusually high, particularly for November.

This high pressure is not a record-setter, though.

“In the contiguous United States, the highest-pressure reading yet measured is 1064 mb (31.42”) at Miles City, Montana on December 24, 1983,” writes weather historian Christopher Burt at Weather Underground. “Many people may remember this as the coldest Christmas in modern U.S. history (at least for almost everywhere east of the Rockies).”